I turned on my good reader after almost 1 year since I was about to sell it and before sending it I wanted to test it was all ok.
I charged it for 3-4 hours before turing it on.
With my big surprise the screen seems somehow damaged. It's like if some e-ink particles are struck on the screen... like when a glass screen breaks but the screen is perfect is just an effect of the e-ink.
I attached the picture. Any suggestion for tests to do before sending back to Booxtor?

I'm certain it's a broken glass. I had a broken device once, and it looked very much like that. Also, that device broke very easily after a tiny drop from about 30 cm. On the other hand my current M92 had much higher drops and has gone through a lot of harmful situations without taking any damage at all.